1. Field of the Invention
The invention relates to a charged particle beam writing apparatus and a charged particle beam writing method, and in particular, relates to an electron beam writing apparatus featuring two aperture shapes and an electron beam writing method of writing using the device.
2. Related Art
Lithography technology assuming the role of advancement for still finer semiconductor devices is, among semiconductor manufacturing processes, an extremely important process to solely generate patterns. In recent years, with ever higher integration of LSI, the circuit line width demanded for semiconductor devices is becoming finer year by year. To form circuit patterns desired on such semiconductor devices, high-precision master patterns (also called reticles or masks) are needed. Here, electron beam writing technology has substantially excellent resolution and is used for the manufacture of high-precision subject copy patterns.
FIG. 12 is a conceptual diagram for illustrating an operation of a variable shaped electron beam writing apparatus.
The variable shaped electron beam (EB) writing apparatus operates as described below: First, a first shaping aperture plate 410 has an oblong, for example, a rectangular opening 411 for forming an electron beam 330 formed therein. Also a second shaping aperture plate 420 has a variable shaped opening 421 for forming the electron beam 330 after being passed through the opening 411 into a desired oblong shape formed therein. The electron beam 330 irradiated from a charged particle source 430 and passed through the opening 411 is deflected by a deflector. Then, the electron beam 330 passes through a portion of the variable shaped opening 421 before a target workpiece 340 mounted on a stage moving continuously in a predetermined direction (for example, the X direction) being irradiated with the electron beam 330. That is, an oblong shape that can pass through both the opening 411 and the variable shaped opening 421 is written in a writing area of the target workpiece 340. A method of creating an arbitrary shape by causing an electron beam to pass through both the opening 411 and the variable shaped opening 421 is called a variable shaped method.
FIG. 13 is a diagram exemplifying a shaped beam.
This is a pattern in which an image 333 passing through the variable shaped opening 421 of a passing image 331 that has passed through the first shaping aperture plate 410 is formed.
In a variable shaped electron beam writing apparatus, as described above, the beam size is adjusted by controlling the position of projection onto the variable shaped opening 421 of the second shaping aperture plate 420 by causing the passing image 331 of the first shaping aperture plate 410 to deflect by a deflector.
FIG. 14 exemplifies a pattern formed by one shot.
FIG. 15A and FIG. 15B are sectional views of process for pattern formation in which a positive type resist is used and a portion where a resist is removed is made a pattern.
As shown in FIG. 15A, a pattern 334 formed by using first and second shaping aperture plates and having a dimension L1 as shown in FIG. 14 is written (exposed) by an electron beam 350 on a positive type resist 361 formed on a substrate 360 such as a mask blank. Then, an exposed portion is removed by development. A resist pattern of the pattern dimension L1 as shown in FIG. 15B can thereby be formed. If a pattern is formed by one shot, as described above, only an error of shaping deflection will affect a dimension error of a pattern. Here, if a value of L1 deviating from the average value <L1> is denoted by δL1, a forming error of the pattern dimension L1 can be shown by: forming error=±δL1. However, when patterns leaving a resist are formed, left and right patterns are written by a writing apparatus and thus, position errors of two shots on both sides will further be added as an error factor.
FIG. 16 exemplifies a pattern formed by two shots.
FIG. 17A and FIG. 17B are sectional views of process for pattern formation in which a positive type resist is used and a portion where a resist is left is made a pattern.
As shown in FIG. 17A, two patterns 335 and 336 formed by using the first and second shaping aperture plates and having the dimension L1 as shown in FIG. 16 are written (exposed) by the electron beam 350 on the positive type resist 361 formed on the substrate 360 such as a mask blank with spacing of L2. Then, an exposed portion is removed by development. Resist patterns of the pattern dimension L2 as shown in FIG. 17B can thereby be formed. Here, if the lower left of each written pattern is defined as a coordinate position, the position of the pattern 335 can be denoted as (x1,y1) and that of the pattern 336 as (x2, y2). Here, the dimension of L2 of the resist pattern can be expressed as L2=x2−x1−l1. If a deviation value δx1 of x1 from the average value <x1> is probabilistically calculated, x1 can be expressed as x1=<x1>+δx1. Here and below, <Q> denotes an average value of Q. Similarly, if a deviation value δx2 of x2 from the average value <x2> is probabilistically calculated, x2 can be expressed as x2=<x2>+δx2. Similarly, if a deviation value δl1, of l1 from the average value <l1> is probabilistically calculated, l1 can be expressed as l1=<l1>+δl1. Then, if a deviation value of L2 from the average value <L2> is denoted as δL2, the relation <δL22>=<L22>−<L2>2=<δx12+δx22+δl12> can be shown to hold. Thus, an error of the pattern dimension L2 can be expressed by: error=√{square root over ( )}(<δx12>+<δx22>+<δl12>). When the positive type resist 361 is used and a pattern is formed by leaving a resist, as described above, there has been a problem that, in addition to a forming error component √{square root over ( )}(δl12), further a position error component √{square root over ( )}(<δx12>+<δx22>) is included, leading to a large error. The error of the dimension L2 of a left pattern, as described above, is worse than that of the dimension L1 of the aforementioned removed pattern and in some cases several times larger.
Thus, if high precision of dimensions of resist patterns is needed in a mask manufacturing process or a wafer process in which a writing apparatus directly writing to a wafer is used, steps described below have been taken. For example, if dimensions are determined by one pattern like a hole pattern, a positive type resist has been used for writing. If, on the other hand, dimensions are determined between two patterns like isolation and gate patterns, a negative type resist is used for writing to make a removed portion a pattern.
FIG. 18A and FIG. 18B are sectional views of process for pattern formation in which a negative type resist is used and a portion where a resist is removed is made a pattern.
As shown in FIG. 18A, the one pattern 334 formed by using the first and second shaping aperture plates and having the dimension L1 as shown in FIG. 14 is written (exposed) by the electron beam 350 on a negative type resist 362 formed on the substrate 360 such as a mask blank. Then, an exposed portion is removed by development. A resist pattern of the pattern dimension L1 as shown in FIG. 18B can thereby be formed. Using a negative type resist can eliminate a position error factor.
It has been necessary, as described above, to use two types of resist, each of which for each purpose. However, using two types of resist has caused many problems shown below.
First, using two types of resist in one process has complicated maintenance and management of the process. As a result, problems such as an operational error being more likely to be invited have been caused. Moreover, an increase in maintenance costs of the line thereof has resulted. As a result, problems such as being a factor of cost increases of a semiconductor apparatus have been caused.
Second, when a negative type resist is used, there has been a problem of swelling and also a problem of difficulty of forming a finer pattern. Thus, there has been a problem that it will be difficult to form a pattern as patterns become increasingly more microscopic in the future. Also, there has been a problem for some type of negative type chemically amplified resist to be more likely to cause waste, creating a problem of causing yield deterioration during pattern formation.
Third, if a negative type resist is used for forming a gate pattern when directly writing on a wafer, an active part of a transistor will be irradiated with electrons. Thus, there is a problem of damage to the transistor.
Here, though not directly related to electron beam writing, a device for forming many identical patterns of the same pitch on a liquid crystal substrate by exposure of light at a time has been disclosed. The device has a first mask having a plurality of openings formed thereon and a second mask having a plurality of openings formed thereon, and light that has passed through the openings of both masks is used for exposure (Refer, for example, to Japanese Unexamined Patent Application Publication No. 2006-145746).
As has been described above, there has been a problem that a dimension error is large for pattern formation in which a positive type resist is used and a portion where a resist is removed is made a pattern. If a negative type resist is used, on the other hand, there has been a problem that other problems described above are caused.